Field device configured for wireless data communication

ABSTRACT

Field devices comprising a transmitter and/or receiver for wireless data communication are provided. The energy available for wireless data communication in data transmitting or data receiving field devices is evaluated prior to activation of the transmitter and/or receiver of the field device.

CLAIM OF PRIORITY

This application is a continuation of U.S. patent application Ser. No.09/983,890, filed on Oct. 26, 2001, the entire contents of which arehereby incorporated by reference.

TECHNICAL FIELD

The present invention relates to a field device for monitoring amanufacturing process and actuating manufacturing process variables, andbeing configured for wireless data communication.

BACKGROUND

Field devices as described in the following are generally used in amanufacturing process to monitor the process and to actuate processvariables. Typically, actuators are placed in the manufacturing field todrive different process control elements, such as valves or sensors.Further, transmitters are installed in the manufacturing field tomonitor process variables, such as fluid pressure, fluid temperature orfluid flow.

Actuators and transmitters are coupled to a control bus to receiveprocess information and transmit the process information to acentralized system controller that monitors the overall operation of themanufacturing process. This control bus may be implemented as a two wirecurrent loop carrying current that provides power supply for operationof a field device.

In such control systems, communication is typically executed through afieldbus standard, which is a digital communication standard thatpermits transmitters to be coupled to only a single control bus totransmit sensed process variables to the central controller. Examples ofcommunication standards include ISA 50.02-1992 Section 11, HART®,Foundation Field Bus, Profibus PA, and FoxCom. HART® overlays digitalcommunication on a 4 to 20 mA process variable signal.

An important aspect with respect to control systems of the type outlinedabove is intrinsic safety. When a field device is located in a hazardousarea without explosion proof equipment, the electronics in the fielddevice should be intrinsically safe, which means that the electronicsmust be designed so that no sparks and no heat are generated therebyeven when one or more electronic component failures occur at the sametime.

Usually intrinsic safety is achieved by employing additional protectiveelements to protect the electronics under a failure condition. Designspecifications and certifications for the protective elements vary withthe specific type of application. For example, they may vary with thetype of explosive gas used within a manufacturing process.

FIG. 1 shows a schematic diagram of a manufacturing process controlsystem. As shown in FIG. 1, the peripheral part of the control systemmay comprise a first intrinsically safe fieldbus segment 10 and a secondbus segment using, e.g., the RS485 standard for data communication. Theintrinsically safe fieldbus segment 10 and the RS485 bus segment 12 arecoupled through a bus coupler 14. Further, the side of the intrinsicallysafe fieldbus segment 10 not being attached to the bus coupler 14 isconnected to a terminating circuit 16 that helps to avoid reflections onthe intrinsically safe fieldbus segment 10.

As also shown in FIG. 1, to each bus segment 10, 12 there is connectedat least one field device 18, 20 and 22. Each field device is either anactuator, a transmitter or another I/O device receiving and/ortransmitting information.

The field devices attached to the intrinsically safe fieldbus segment 10may be powered through an electric current received from theintrinsically safe fieldbus segment 10 leading to a voltage drop acrossthe field devices 20, 22. Typically, the intrinsically safe fieldbussegment 10 will be operated under a fieldbus protocol or any otherappropriate protocol allowing to exchange digital information.

As shown in FIG. 1, the field devices 20, 22 coupled to theintrinsically safe fieldbus segment 10 exchange information throughmodification of the current flowing into each single field device 20,22. For digital communication, a basic value of the current of theintrinsically safe fieldbus segment 10 is modulated to be increased ordecreased by a predetermined offset value, i.e. 9 mA for the fieldbusstandard. This modulation of the current flowing into either the fielddevice 20 or the field device 22 leads to a modification of a voltage UBon the intrinsically safe fieldbus segment 10 thus achieving digitalcommunication.

FIG. 2 shows a more detailed schematic circuit diagram of a field deviceshown in FIG. 1. As shown in FIG. 2, the intrinsically safe fieldbussegment 10 may be summarized into an equivalent circuit diagram with anideal voltage source 24 and a resistor 26 to model AC voltage impedanceand to fulfill intrinsic safety requirements for spark protection,current limitation and power limitation in a hazardous area. As alsoshown in FIG. 2, each field device is connected to the intrinsicallysafe fieldbus segment with two lines 28, 30 being also connected to adischarge protection unit 32. At the output of the discharge protectionunit 32 there is provided a modulating unit 34 which allows modulationof the operating current flowing into the field device.

The modulating unit 34 is connected in series to a power converter unit36 that is adapted to map the operating current flowing over themodulating unit 34 into a suitable power supply signal for a controlunit 38 connected to the output of the power conversion unit 36. Thecontrol unit 38 is connected to an actuator and/or sensor unit 40 forthe control thereof.

Operatively, the controller unit 38 controls the operating currentmodulating unit 34 to achieve a modulation of the operating current andtherefore exchange information between the intrinsically safe fieldbussegment 10 and the field device. Further, the control unit 38 hascontrol over the further elements in the field device.

Operatively, each field device 20, 22 connected to the intrinsicallysafe fieldbus segment 10 receives an operating current from theintrinsically safe fieldbus segment 10. During transfer of informationfrom the field device to the intrinsically safe fieldbus segment 10, thecurrent value for the operating current is determined by the modulatingunit 34 under control of the control unit 38. Further, to receiveinformation at the field device, the controller unit 40 maintains theresistance of the modulating unit 34 at a constant value. When adifferent field device triggers a change of the voltage on theintrinsically safe fieldbus segment 10, the remaining field device(s)connected to this intrinsically safe fieldbus segment 10 may detect thischange of a voltage through the connection lines 28, 30 for furtherprocessing thereof in the control unit 38. This digital communicationmechanism is used to provide the controller unit 40 in each field deviceboth with control information for activation of actuators and/or sensorsduring manufacturing process control and surveillance of the fielddevice itself.

It becomes clear that explosion protection in a hazardous area andshortage of energy supply are currently the major constraints for theoperation of field devices. Therefore, different approaches to ignitionprotection in hazardous areas exist, e.g., an explosion intrinsicallysafe fieldbus, passive achievement of intrinsically safety throughrelated design of electronics to avoid overheating and increasedcurrents/voltages, or active implementation of intrinsic safety usingactive electronic devices such as electronic limiters. For reasons ofexplosion protection, if the electronics of a field device are notintrinsic safe, encapsulation into mechanically stable housings andsealed conduits and pipes for electric cables are required to achieveexplosion protection, independent from the electronic design. To supportboth protection systems with one type of device, intrinsicly safeelectronic and explosion proof mechanical design must be combined in onefield device.

In conclusion, the exchange of information and the access to sensors inthe field device is severely limited both from a mechanical but alsofrom an electrical point of view and only limited transfer rates areachievable.

In other words, higher transfer rates in a two wire implementation wouldnormally lead to an unacceptable current consumption in view ofavailable power supply all through the control bus. These restrictionsare becoming even more severe in view of the fact that control buses andcurrent loops will be operative with even more reduced currents—e.g., aslow as 3.6 mA.

SUMMARY

In one general aspect, a field device includes at least one actuatorand/or sensor adapted to alter and/or sense a control and/or processvariable in a manufacturing field, a transmitter and/or a receiverconfigured to provide wireless data communication, and a controller. Thecontroller is configured to evaluate the energy available in the fielddevice for wireless data communication prior to activation of thetransmitter and/or receiver.

These and other aspects permit an increase in the data exchangecapabilities of field devices without sacrificing intrinsic safety. Inparticular, wireless data communication may substitute or supplementwirebound communication in a manufacturing field (where a constraint isreduced power supply) through the use of appropriate power management.In particular, the wireless data exchange may be easily combined withthe data exchange over a control bus so as to increase the overallbandwidth for communication in each field device.

Using wireless data transmission directed to the field device, anincrease in bandwidth may be achieved without any increase ininstallation expenditure as no additional wiring is required in themanufacturing field. Further, wireless communication does not requirethe matching to specific impedances for the exchange of communicationsignals, thus avoiding the consideration of impedances and sparkprotection at system input and/or output terminals to achieve intrinsicsafety according to the usual technology.

The adaptation of wireless data transmission for field devices throughappropriate power management allows field devices to be operatedexclusively through wireless communication using a configurator. Thispromises to avoid potential problems with respect to the intrinsicsafety and also to decrease the associated costs.

When using wireless data transmission alone, the problem of anintrinsically safe coupling of the control bus in the manufacturingfield is eliminated. Here, it is important to note that the energynecessary for wireless data communication will never reach a levelsufficient to ignite an explosive gas mixture. Yet another decisiveadvantage of wireless data communication is that electrical contacts ofthe field devices do not need to be exposed.

In some implementations, the exchange of data using wirelesscommunication from and/or to the device may be delayed in the event thatan energy shortage in the field device would lead to an unsafe datatransfer. The delay time may be used to supply further energy to thefield device before activation of the transmitter and/or receiver. Thispermits guaranteed safe exchange of data from and/or to the fielddevice. Since data communication only starts when enough energy isavailable in the field device, any interruption of a data exchange afterinitiation thereof and therefore any loss of energy in the field devicedue to uncompleted data exchange processes may be strictly avoided.

The data stream to be transmitted and/or received through wireless datacommunication may be split into separate data segments. Through thistechnique, unnecessary delays during the data transmission and/orreception may be avoided. In other words, since less energy is necessaryfor smaller data packages or data segments, the transfer and/orreception thereof may be initiated when only a small amount of energy isavailable in the field device. Overall, this leads to an acceleration ofthe wireless data transmission and/or reception.

The transmitter and/or receiver may be of the infrared type and mayinclude a coder unit adapted to receive an input bit stream and to codeeach input bit such that a related, generated coded pulse has a pulsetime period shorter than the bit pulse time period. This approach topower consumption reduction is not restricted to a particular codingscheme. In other words, either a logical 1-bit or a logical 0-bit may becoded into a narrower coded pulse while the logical 0-bit or 1-bit isnot coded into a pulse at all. Also, transitions between different bitpulse amplitudes 1, 0 may be coded into pulses for subsequent outputthereof.

Coded pulses may have different widths or frequencies for indication ofeither one of two states, i.e., logical 1, 0 or a transitiontherebetween. The techniques may also be adapted to the IrDA Standardpublished by the Infrared Data Association Organization as a standardfor serial infrared data exchange.

The described techniques allow for an interoperable, low-cost,low-power, half duplex serial data interconnection standard to beapplied within manufacturing fields to produce, retrieve, present andtransmit control information and sensor and/or actuator-relatedinformation.

This new approach to a cost efficient cordless user interface in themanufacturing field, in particular the IrDA Standard, also enables theintegration of personal digital assistance with PDA, desktop andnotebook computers as configurators or remote device in suchmanufacturing plants. These available standard components thereforereduce the overall costs of system implementation. Further standards tobe applied within the framework of the described techniques are theserial infrared link SIR, the link access protocol IrLAP and the linkmanagement protocol IrLMP to extend the bandwidth to up to 4.0 Mbit/s.Further, the techniques are well adapted to future extensions of lowpower transmission standards as long as the infrared transmissionrequires only a relatively small power supply.

However, it should be noted that the described techniques are notrestricted to infrared transmission of data alone. To the contrary,wireless data communication may also be achieved in the radio, visiblelight or ultrasonic frequency range to replace cable connecting portableand/or fixed field devices.

The transmitter may include a transmitting unit (either for infraredvisible light, ultrasonic or radio frequency) connected between a powersupply line and ground and an energy buffer coupled across the lightemitting unit for supply of energy thereto. This accounts for thereduced availability of power within the field device. In other words,when the transmitting unit is not emitting waveforms, energy availableon the power supply line may be pre-stored in the energy buffer (e.g., acapacitor) for subsequent use during the transmission process. This isparticularly useful when the power supply line does not supplysufficient energy to the transmitting unit during transmission so thatthe energy buffer backs up the power supply.

The transmitter may further include a first resistor and a secondresistor connected in series between the power supply line and thetransmission unit. The energy buffer is connected to the node betweenthe first resistor and the second resistor and the second resistor isvariable to change, e.g., the irradiance of a light-emitting unit usedfor wireless transmission or the output power of a radio frequencytransmitter. The first resistor serves to limit the amount of energy orthe maximum current flowing into the energy buffer and the secondresistor allows for adaptation of the transmission range, e.g.,according to available energy within the field device or according to adesired data exchange distance. Therefore, the field device may be usedtogether with the remote configurator such that different data exchangedistances may be specified for different operative conditions. Oneexample would be that in a hazardous environment an operator may notapproach the field device beyond a predetermined limited distance whilein other environments he may closely approach the field device to reducethe amount of power consumed during data exchange.

The techniques described above may be implemented in a manufacturingplant control system that includes at least one functional unit coupledto a central controller by a system bus, and at least one control buscoupling at least one field device to the functional unit. The at leastone field device includes a transmitter and/or receiver adapted tocommunicate using wireless data communication with a remote device, anda controller adapted to evaluate the energy available in the fielddevice for wireless data communication prior to activation of thetransmitter and/or receiver.

Wireless data communication may be used to configure, interrogate,calibrate or test field devices without touching them, and to substitutewireless communication links for the control bus. In other words, whenall communication is achieved in a wireless manner, one can implementthe control system for the manufacturing process without any wiring inthe manufacturing field at all or through a combined form ofcommunication links, i.e., through the control bus and wireless infraredcommunication links.

Different field devices or functional units of the manufacturing plantcontrol system may each have a transmitter linked through a remoteaccess data exchange network. The provision of a remote access dataexchange network allows for remote data exchange in a very efficientmanner. In another variation, only a single field device or functionalunit has a wireless data communication capability and is used as anaccess point or portal for access to various components in themanufacturing field that are connected to the same control loop as thefield device serving as portal. The application of the portal concept toa manufacturing field allows a reduction in the effort and expensenecessary to achieve wireless data communication.

In another general aspect, exchanging data in a manufacturing fieldusing wireless data communication includes evaluating the energyavailable for wireless data communication in a data transmitting or datareceiving field device prior to activation of a transmitter and/orreceiver of the field device. This allows the advantages outlined aboveto be achieved. Also, input data may be divided into data segments withan idle time in between. Therefore, the transmitting and/or receivingfield device may be supplied with further power for subsequent wirelessdata transmission during each idle time.

Yet another important advantage of the segmentation of the input datastream into smaller data segments is that prior to the transmissionand/or reception of each data segment it is possible to check on theavailable energy for data exchange. When the energy available within thefield device is insufficient for the requested data exchange, the dataexchange may be delayed until enough energy is available. This allowsavoidance of data loss or an incomplete and therefore faulty dataexchange in the manufacturing plant control system which might possiblylead to failures.

The energy available in the field device for wireless data communication(e.g., a voltage of a buffer capacitor) may be monitored and thewireless data exchange may be stopped when the energy supply is nolonger sufficient. This allows the exchange of data using wirelesscommunication as long as energy is available in the field device.

A computer program product directly loaded into the internal memory of afield device controller may include software code portions for use inexchanging data in a manufacturing field using wireless datatransmission when the computer program product is run on the fielddevice controller. Such an implementation leads to the provision ofcomputer program products for use within a computer system or morespecifically a processor comprised in, e.g., a controller of atransmitter and/or receiver.

Programs defining the method functions can be delivered to a controllerin many forms, including but not limited to information permanentlystored on non-writable storage media, e.g., read only memory devicessuch as ROM or CD ROM discs readable by processors or computer I/Oattachments; further information stored on writable storage media, i.e.,floppy discs and hard drives; or information conveyed to a controllerthrough communication medias such as network and/or telephone networkand/or Internet through modems or other interface devices. It should beunderstood that such media, when carrying processor and/or controllerreadable instructions represent alternate implementations.

The details of one or more implementations are set forth in theaccompanying drawings and the description below. Other features will beapparent from the description and drawings, and from the claims.

DESCRIPTION OF DRAWINGS

FIG. 1 shows a peripheral part of a manufacturing process controlsystem.

FIG. 2 shows a more detailed schematic diagram of the field devicesshown in FIG. 1.

FIG. 3 shows a schematic diagram of a field.

FIG. 4 shows a schematic diagram of another field device.

FIG. 5 shows a schematic diagram of a transmitter and/or receiver forwireless data communication.

FIG. 6 shows a schematic diagram of the controller of the transmitterand/or receiver shown in FIG. 5.

FIG. 7 shows a circuit diagram of an infrared transmitter.

FIG. 8 shows a circuit diagram of an infrared receiver.

FIG. 9 shows coding schemes used for data exchange via infraredtransmission and/or reception.

FIG. 10 shows a frame format used for data exchange via infraredtransmission and/or reception.

FIG. 11 shows the relation between the irradiance of the infraredtransmitter and an achievable data exchange distance.

FIG. 12 shows a relation between a radiant intensity of the infraredtransmitter and an angle of emission.

FIG. 13 shows a circuit diagram of a radio frequency transmitter.

FIG. 14 shows a circuit diagram of a radio frequency receiver.

FIG. 15 shows a flowchart for a method of transmitting data.

FIG. 16 shows a flowchart for a method of receiving data.

FIG. 17 shows a schematic diagram of a manufacturing plant controlsystem using unidirectional wireless data transmission.

FIG. 18 shows a schematic diagram of another manufacturing plant controlsystem using bidirectional wireless data transmission.

FIG. 19 shows a flowchart for a method of handling wireless datatransmission bottlenecks in the manufacturing plant control system shownin FIG. 18.

FIG. 20 shows a schematic diagram of yet another manufacturing plantcontrol system with field devices having sensors of different types.

FIG. 21 shows a schematic diagram of yet another manufacturing plantcontrol system using a remote access to field devices via wirelesscommunication.

FIG. 22 shows a schematic diagram of yet another manufacturing plantcontrol system using a remote access network to link differentsub-systems having a wireless transmitter and/or receiver.

Like reference symbols in the various drawings indicate like elements.

DETAILED DESCRIPTION

FIG. 3 shows a schematic diagram of a field device. Those elementshaving the same reference numeral as corresponding or related elementsshown in FIG. 2 will not be explained in detail in the following, butreference is made to the explanation of FIG. 2 as outlined above.

As shown in FIG. 3, the field device differs over previously known fielddevices in that it comprises a transmitter and/or receiver 42 forwireless data communication. Further, there is provided a display unit44, e.g., a LCD device, for display of measurement of control data tothe user of the field device. The transmitter and/or receiver 42 and thedisplay unit 44 are arranged behind a transparent window 46 provided inthe housing of the field device.

As also shown in FIG. 3, the field device may communicate with theremote device 48 having as well a transmitter and/or receiver 52 forwireless data communication and a display unit 54 arranged behind atransparent window 56. This remote device may be used, e.g., forinterrogation, configuration, calibration and testing of the fielddevice. The display units display measured or transferred variables aswell as menus and fully descriptive messages. Further, self-consistingmenus allow rapid execution of testing steps. The remote device may be alaptop computer, a hand-held PC, a PDA assistance, a mobile telephone orany other appropriate portable communication unit adapted to wirelessdata communication. Standard devices may be used instead of specificallydesigned hardware to reduce overall system costs in comparison towirebound communication.

Further, dependent upon the application it might be necessary that theremote device is either intrinsically safe or explosion proof or both.Here, intrinsic safety is easier to achieve than explosion proofness asin the latter case the operating elements must be provided in anexplosion proof remote device housing. However, one feature is that theremote device as such must not be wired with the field device thusavoiding an explosion proof encapsulation of electrical contacts.

As shown in FIG. 3, operatively the transmitter and/or receiver 42 andthe display unit 44 are operated under control of the controller unit 38of the field device. The energy necessary for the operation of thetransmitter and/or receiver 42 and the display device 44 is suppliedexternally via the control bus, the discharge protection unit 32, andthe DC/DC converter 36.

FIG. 4 shows a schematic diagram of another field device. Here the samecorresponding parts as outlined above with respect to FIG. 3 or denotedusing the same reference numerals and the explanation thereof will beomitted.

As shown in FIG. 4, the field device is of the stand-alone type andpower supply is achieved through an internal power source 58. Also,exchange of information is based solely on the wireless link between thefield device and the remote device 48 without any exchange ofinformation over a control bus. Hereby efforts for wiring the controlbus in the manufacturing field become obsolete.

FIG. 5 shows a schematic diagram of the wireless transmitter and/orreceiver as shown in FIGS. 3 and 4 in more detail. It should be notedthat any functionality to be described in the following may be realizedin hardware, in software or a combination thereof.

As shown in FIG. 5, the transmitter and/or receiver 42, 52 divides intoa controller section with a controller 60 and a buffer memory 62.

In the transmission path of the transmitter and/or receiver there isprovided a coder 64 receiving data to be transmitted and driving adownstream transmitter 66.

In the reception part of the transmitter and/or receiver there isprovided a receiver 68 being supplied with a transmission waveform andfeeding pulses to a downstream decoder 70 for decoding into an outputbit stream. The coder 64 and the decoder 70 form part of a modemsection, and the transmitter 66 and the receiver 68 form part of atransceiver section.

FIG. 6 shows a schematic diagram of the controller of the transmitterand/or receiver shown in FIG. 5.

As shown in FIG. 6, the controller 60 divides into a protocol drivingunit 72, a coder and/or decoder control unit 74, an interface unit 76and an input/output interface unit 78.

Operatively, the protocol driving unit 72 stores different physicallayer protocols used for transmission and/or reception and the exchangeof information via the control bus. Further, the coder and/or decodercontrol unit 74 achieves a selection of an appropriate coding scheme tobe used in the coder 64 in the related decoding scheme for use in thedecoder 70. The interface unit 76 is provided to control the pulsewaveform in the transmitter in compliance with a required data exchangedistance and wireless transmission and/or reception conditions. Theinput and/or output interface unit 76 serves to set up an interface tothe user of either the field device or the remote unit. The input and/oroutput interface unit is adapted to drive the display units 44, 54 forcontrol of data input and/or output to the field device and/or remotedevice via a keyboard and further to the mapping of alpha numeric inputdata to an internally used data format.

As will be outlined in the following, wireless data communication may beachieved either in the infrared frequency range, in the radio frequencyrange, in the frequency range of visible light, or in the ultrasonicfrequency range. In the following, the wireless infrared datacommunication will be explained with respect to FIGS. 7 to 12 and thewireless radio frequency transmission will be explained with respect toFIGS. 13 and 14.

FIG. 7 shows a circuit diagram of an infrared transmitter. As shown inFIG. 7, the infrared transmitter has a power supply line 80 and a groundline 82. The infrared transmitter comprises a driver amplifier 84 havinga first power supply terminal connected to the power supply line 80 anda second power supply terminal connected to ground line 82. Between thepower supply line 80 and the ground line 82 there is provided a firstresistor 86, a second resistor 88, a light emitting element—e.g., alight emitting diode—90, and a switching transistor 92 connected inseries. At the node connecting the first resistor 86 and the secondresistor 88 there is provided a capacitor 94 branching off to ground.Across the capacitor 94 there is connected a voltage detector 96 formeasurement of the voltage across the capacitor 94 and therefore of theenergy suppliable by the capacitor 94.

Operatively, the infrared transmitter shown in FIG. 7 emits infraredwaveforms according to power supplied to the driving amplifier 84. It isproposed to provide the capacitor 94 for intermediate energy storagewhen no power is consumed by the light emitting element 90. This allowsto supply additional energy to the light emitting element 90 duringinfrared waveform transmission in case the energy supplied by the powersupply line 80 is smaller than the infrared waveform transmissionenergy. The provision of the capacitor 94 is of particular advantagewhen using the infrared transmitter in a field device having restrictedresources of power supply.

Further, the provision of the voltage detector 96 allows to alwaysevaluate the energy available to the capacitor 94 and therefore aprecise control of the operation of the transmitter shown in FIG. 7.

The first resistor 86 is provided to achieve a smooth energy flow fromthe power supply line 80 to the capacitor 94. The second resistor 88 isvariable and tuned according to a desired irradiance of thelight-emitting element 90 and according to a predetermined data exchangedistance. The capacitance of the capacitor 94 is typically smaller than100 mF, e.g., 68 mF and the resistance of the first and second resistor86, 88 is smaller than 120 W and 10 W, respectively.

FIG. 8 shows a circuit diagram of an infrared receiver 68. As shown inFIG. 8, the infrared receiver comprises a light-receiving unit 98 (e.g.,a photo diode) and a filter 100 connected thereto in series. The filter100 is provided to filter out those components in the received infraredwaveform signal that are not related to the transmission of data but tointerfering signals, e.g., ambient light.

In the following coding schemes for wireless infrared communication willbe described with respect to FIG. 9. It is to be noted that the codingschemes to be described hereinbelow are to be considered as examplesonly and that any physical layer having the characteristic to reduce thepower consumption in comparison to an input bit stream may be used.While FIG. 9 shows different approaches to an appropriate coding it isfurther to be noted that clearly also a combination of these codingschemes is as well applicable within the framework of the describedtechniques.

The coding and/or decoding scheme shown in FIG. 9(a) relies on the ideato code only one of two input bits in the input data stream. The codedbit is assigned a pulse having a reduced pulse time period in comparisonto the related bit pulse time period. While according to the codingscheme shown in FIG. 9(a) the L-bit is coded into pulse P1 with a pulsetime period T1 the coding scheme shown in FIG. 9(b) uses a coding of theH-bit into a pulse P2 with a pulse time period T2.

The coding and/or decoding scheme shown in FIGS. 9(a), 9(b), are relatedto a physical layer IrDA where the ratio between the pulse time periodof the coded pulse and the bit time period is 3/16.

This implementation has many advantages in the sense that any standardcomponents available for this IrDA data transmission standard may easilybe adapted to control applications in manufacturing fields without anycompatibility problem.

Further, it enables the use of sub-standards published for the IrDaStandard i.e., the serial infrared link specification SIR, the linkaccess protocol specification IrLAP and the link management protocolspecification IrLMP. Also, it enables the use of extensions to the IRDAStandard with high-speed extensions of 1.152 Mbit/sec and 4.0 Mbit/secwhile maintaining low power consumption essential for the operation ofthe field devices.

Yet another option within the IrDA standard framework is the use of theIrBus (or CIR (standard)) using the EC 1603-1 sub-carrier frequencyallocation with a carrier at 1500 kHz and having a transmission capacityof 72 kbit/sec.

Yet another option is the advanced IR standard (AIR 256 Kbit/sec, 7meter exchange coverage) and the fast IR standard (FIR, minimum transferrate of 16 Mbit/sec over more than 1 meter data exchange distance).

Further, IrDa physical layer enables to run any protocol such as FoxCom,HART, Profibus, Foundation Fieldbus, etc. between the field device andthe remote device. In case the IrDA physical layer is used it ispossible to integrate standard components into the manufacturing controlsystem such as RS 232 interfaces.

FIG. 9(c) shows another coding and/or decoding scheme that may be used.Here, each transition from a L-bit to a H-bit is coded using a pulse P3with a pulse time period T3 while each reverse transition from a H-bitto a L-bit is coded using a pulse P4 having a pulse time period T4>T3.

FIG. 9(d) shows a coding scheme where each L-bit is coded to a codedpulse P5 such that in response to this coded pulse P5 the infraredtransmitter 66 transmits an infrared waveform having a first frequencyf1. Each H-bit is coded with a pulse P6 such that in response to thiscoded pulse P6 the infrared transmitter 66 transmits an infraredwaveform having a second frequency f2.

FIG. 9(e) shows a coding scheme where each transition from a L-bit toH-bit is coded into a pulse P7 such that in response to this pulse theinfrared transmitter 66 transmits an infrared waveform having a thirdfrequency f3. Also, each transition from a H-bit to L-bit is coded to apulse P8 such that in response to this pulse the infrared transmitter 66transmits an infrared waveform having a fourth frequency f4.

Further alternatives to code and/or decode two different bit levels 0, 1(not shown) are the use of two light emitting diodes operating at twodifferent frequencies. Here, each single light emitting diode would beassigned either to a first and second bit level or to a first and secondtransition between different bit levels. Yet another variation of thecoding and/or decoding schemes shown in FIG. 9 would be to use aplurality of pulses with reduced pulse time periods for each state to becoded as long as a reduced power consumption is achieved.

FIG. 10 shows a frame format used for data exchange via infraredtransmission and/or reception. As shown in FIG. 10, coding may not onlybe carried out with respect to single data bits in an input data streambut also in compliance with a predetermined frame format, i.e. the UARTframe format (universal asynchronous receiver/ transmitter standardknown from the field of personnel computation). While FIG. 10 shows theapplication of the coding scheme according to FIG. 9(a) to such a UARTframe format it is to be noted that clearly any other coding schemeshown in FIG. 9 or any combination thereof may as well be applied to aframe format based coding scheme.

An important advantage with respect to the use of a frame format is thatthe input data stream may be segmented into input data segments forstorage in the buffer memory 62 of the infrared transmitter and/orreceiver shown in FIG. 5. In other words, it is proposed to divide theinput bit stream into smaller segments which are then transmitted insequence over time. This is of particular importance with respect tofield devices since during transmission of data the energy stored in thefield device will gradually decrease due to current consumption in thefield device for the transmission process. When a data segmentation inthe sense outlined above is used, the field device may receive furtherpower from the control bus between two subsequent data segments tomaintain infrared waveform transmission.

FIG. 11 shows a relation between the irradiance of the infraredtransmitter and an available data exchange distance. As already outlinedabove the irradiance of the infrared transmitter may be derived bytuning the second resister 84 shown in FIG. 7 and therefore by tuningthe current flowing over the light emitting element 90.

FIG. 11 allows to determine the data exchange distance as a function ofthe irradiance at the infrared transmitter. Assuming that a minimumirradiance at the receiver is 40 mW/m2 combined with an intensity of 40mW steradian (3r) the resulting data exchange distance is 1 m. In casethe minimum irradiance at the receiver is 100 mW/m2 with the sameintensity of 40 mW/sr the data exchange distance will only be 70 cm. Inthe same way, achievable data exchange distances may be derived from thediagram shown in FIG. 11 for different transmitter irradiance values andintensities.

FIG. 12 shows a relation between a radiant intensity of the infraredtransmitter and an angle of emission. As shown in FIG. 12, the opticalradiant intensity should be limited to a maximum value, e.g., 500 mW/srand an angle of +30° to enable an independent operation of more than onefield device or remote device in the manufacturing field. Heretofore,FIG. 12 shows a tolerance field scheme for infrared transmitter emissioncharacteristics and typical emission curves of infrared transmitters.

In the following, a transmitter and/or receiver for wireless datacommunication in the radio frequency range will be explained withrespect to FIGS. 13 and 14. Here, it should be noted that the principlesfor coding an input data stream as explained with respect to infraredwireless data communication are as well applicable to the wireless dataexchange in the radio frequency range. Further, those parts shown inFIG. 13 being identical to those previously discussed with respect toFIG. 7 are denoted using the same reference numerals and the explanationthereof will be omitted.

As shown in FIG. 13, in case wireless data communication is executed inthe radio frequency range, there is provided a radio frequencytransmitter 102 in series to the first resistor 86. This radio frequencytransmitter 102 substitutes the second resistor 88, the light emittingdiode 90, the switching transistor 92, and the driving amplifier 84shown in FIG. 7.

Operatively, the radio frequency range transmitter shown in FIG. 13 usesthe first resistor 86 to restrict the current to the energy buffer 94.The voltage detector 96 is provided to measure the energy suppliable bythe capacitor 94. Control data and input data are supplied to the radiofrequency range transmitter 102 before subsequent transmission of theinput data. The radio frequency range transmitter may have a programmerpower control input terminal receiving digital input data to determinethe output power of the transmitter 102.

FIG. 14 shows the structure of a radio frequency receiver. As shown inFIG. 14, the radio frequency receiver divides into a receiver section104 and a demodulator section 106. Operatively, the receiver section 104transmits a radio frequency signal into an intermediate frequency orbase band signal for subsequent processing by the demodulator 106.

As already outlined above, also for the wireless communication withradio frequency the receiver section may be operated in compliance withthe energy available for wireless data reception. In other words, thereceiver section may be activated and/deactivated into a standby modeuntil either enough energy is available for wireless data reception orduring wireless data transmission. Another alternative is that it isrecognized at the receiver that the received address is not related tothe field device comprising the receiver section. Yet anotheralternative is to put the receiver section into a standby mode duringthe setup of a response to be transmitted by the field device afterreceiving a request for data transmission. The use of a standby mode inthe receiver section in accordance with difference operative conditionsallows to reduce the current consumption of the receiving section from,e.g., a range of 20 mA to 60 mA to only some μA.

It should be noted, while in the above the infrared and radio frequencytransmission have been described separately, it is clearly possible tocombine both transmission methods within a certain application.

Further, it should be noted that the concepts explained with respect towireless data communication may as well be applied to the change of datausing visible light and the ultrasonic frequency range.

In the following, the method of exchanging data in a manufacturing fieldusing wireless transmission will be described with respect to FIGS. 15and 16.

FIG. 15 shows a flowchart for a method of transmitting data. As shown inFIG. 15, initially in step S1 the next data block stored in the buffermemory 62 is identified to check for further transmission data. Then, aninterrogation takes place in step S2 to check whether data to betransmitted is identified in the first step S1. If this is not the case,the procedure ends. Otherwise, a bit wise transmission of each bit inthe identified data block is carried out in step S3. Step S3 dividesinto the derivation of a bit value in step S31, the coding or modulationof the bit in step S32 according to, e.g., one of the coding schemesoutlined above with respect of FIG. 9, and a subsequent wirelesstransmission in Step S33.

As shown in FIG. 15, after transmission of each bit there follows aninterrogation in step S4 whether all bits of a data block have beentransmitted. In the affirmative case the procedure returns to step S1 tocheck for further data to be transmitted.

When data is transmitted from a field device to a remote device or afurther remote unit in the manufacturing control system it is checked inStep S5 whether enough power for further data transmission is available.If this is the case, the procedure returns to step S3 for transmissionof the next data bit. Otherwise, the transmission process is delayed instep S6 until supply of further energy to the field device. Thisevaluation of available energy before data transmission allows to avoidany loss of data during data transmission.

FIG. 16 shows a flowchart for a method of receiving data. As shown inFIG. 16, initially a data exchange setup is identified in step S7 beforethe reception of actual data. Then follows an interrogation step S8 toevaluate whether more data is received or not. If this is not the casethe procedure ends. Otherwise, data is received, e.g., bit by bit instep S9. This reception step S9 divides into a first step S91 forwaveform reception, a step S92 for decoding or demodulating the receivedwaveform, and step S93 to derive the received bit value. Subsequent toeach data bit reception step S9 there follows the storage of the newdata bit in step S10.

As shown in FIG. 16, in case the field device is receiving data eitherfrom a remote device or another transmitter in the manufacturing controlsystem after each step S10 to store received data there follows aninterrogation in step S11 to check whether enough energy for furtherdata reception is available in the field device. In the affirmative casethe procedure branches back to S8 to check whether more data isreceived. Otherwise, the field device will indicate energy shortage tothe transmitter for delay of data reception until supply of furtherenergy to the field device in step S12.

While in the above aspects of wireless transmission with respect tocoding and/or decoding and implementation of wireless transmission infield devices have been discussed with respect to FIGS. 3 to 16 in thefollowing system aspects and the use of the wireless transmission withina manufacturing control system will be discussed with respect to FIGS.17 to 22.

FIG. 17 shows a schematic diagram of a typical manufacturing plantcontrol system using unidirectional wireless data transmission. Themanufacturing plant control system comprises a central controller (notshown) coupled to a system bus 108. To the system bus 108 there iscoupled at least one functional unit 110 comprising, i.e., bus couplersor master units for control of attached field devices. As shown in FIG.17, the functional unit 110 is connected to a plurality of fielddevices, 112, 114 and 116 via control buses 118, 120 and 122,respectively.

As also shown in FIG. 15, the field device 112 is connected to a pump124 in a fluid path, the field device 114 is connected via an actuator126 to a control valve 128, and the field device 116 is connected to aflow rate sensor 130. Each field device 112, 114, 116 is provided with awireless data communication transmitter and/or receiver so that a remotedevice 132 may be used for data exchange, i.e. for configuration,display of sensor data and testing purposes.

Operatively, the manufacturing plant control system shown in FIG. 17achieves a control of the fluid flow rate through data exchange over thesystem bus 108 and the control buses 118, 120 and 122. This allows tocontrol the pump 124, the control valve 128 and forward the measuredflow rate from the flow rate sensor 130 back to the system controller:

Further, it is also possible to have access to the different fielddevices 112, 114 and 116 for configuration, display of sensor data ortesting purposes. As also shown in FIG. 17, a field device 114 may alsodirectly communicate with a wireless transmitter and/or receiver 134 ofthe functional unit 110.

The provision of wireless communication links allows to increase theavailable bandwidth for data exchange and facilitates the access tofield devices for an operator running the manufacturing plant controlsystem.

FIG. 18 shows a schematic diagram of another manufacturing plant controlsystem using bi-directional infrared data exchange. Those elements beingidentical or corresponding to the one previously discussed with respectto FIG. 17 are denoted using the same reference numerals and theexplanation thereof will be omitted.

As shown in FIG. 18, this further manufacturing plant control systemuses bi-directional wireless communication instead of unidirectionalwireless communication. Therefore, it is possible to omit control busesand to build up the control system downstream the functional unit 110using wireless communication only. Heretofore, only a DC power supply136 to each field device 112, 114 and 116 must be provided for.

As shown in FIG. 18, using bi-directional wireless communication eachfield device 112, 114 and 116 may directly communicate with at least onetransmitter and/or receiver 134 provided in the functional unit 110.Also, wireless data exchange may as well occur between different fielddevices, i.e., the field devices 112 and 114 or the field devices 114and 116. The routing of wireless data communication over different fielddevices is particularly advantageous in case an obstacle blocks a directdata exchange between the functional unit 110 and the field devices 112,114, 116.

FIG. 19 shows a flowchart for a method of handling wireless datatransmission bottlenecks/obstacles in the manufacturing plant controlsystem shown in FIG. 18. As shown in FIG. 19, initially there is carriedout an interrogation step S13 to check whether more data is to beexchanged. Then follows a data transmission and/or reception step S14followed by a further interrogation in step S15 to check whether thedata exchange has been successful. In the affirmative case the procedurereturns to step S13. Otherwise, an additional interrogation takes placein step S16 to check whether a time out has occurred i.e., whethermultiple tries for data transmission and/or reception did not lead tothe required exchange of data. If this is the case, the procedure stops.Otherwise, another route for data exchange is selected in step S17 andthe procedure returns to step S14 for further data transmission and/orreception.

FIG. 20 shows a schematic diagram of yet another manufacturing plantcontrol system with field devices having sensors of a different type. Asshown in FIG. 20, field devices may be used with a plurality of sensors,i.e., field device 138 with respect to a pressure sensor 140 and fielddevice 142 with respect to a pH sensor 144. Also, it is possible toaccess these further pressure sensor 140 and pH sensor 144 in a remotemanner via the remote terminal 132, the field device 116 and thefunctional unit 110 and the further functional unit 146. This isparticularly advantageous in case the operator or the remote device 132also needs information about a pressure and/or pH value without havingthe possibility of direct access to the related field devices 138, 142.

FIG. 21 shows a schematic diagram of yet another manufacturing plantcontrol system using an indirect access to field devices via wirelesscommunication. As shown in FIG. 21, the remote device 132 has access toa transmitter and/or receiver 147 provided in, e.g., the master of thefunctional unit 110. Data is exchanged with field devices 148, 150having no transceiver and/or receiver for wireless data communicationvia a field bus 152 or any network logically or physically coupled tothe fieldbus.

Another variation to the implementation shown in FIG. 21 would be that aplurality of field devices are connected to the fieldbus 152. One of thefield devices is provided with a transceiver and/or receiver forwireless data communication and therefore allows to achieve a remoteaccess to all other field devices being linked to the field bus 152. Inother words, the field device comprising the transmitter and/or receiverfor wireless communication would be used as access point or portal forremote access for all remaining field devices being linked to thefieldbus 152.

FIG. 22 shows a schematic diagram of yet another manufacturing plantcontrol system having a remote access network 154 to link differentcomponents provided with a transmitter and/or receiver for wireless datacommunication. As shown in FIG. 22, the manufacturing plant controlsystem using the remote access network 154 differs over the previouslydiscussed systems in that the remote access network is provided asdedicated link between different devices having a transmitter and/orreceiver for wireless data communication. This is particularlyadvantageous in case a remote access is required also when othercommunication channels (i.e., the control bus) are not available, i.e.due to lack of power supply. Typically, a request for data exchangewould indicate the source ID of the remote device initiating therequest, further the target ID of the field device to which the remoteaccess is carried out, and data specifying operations to be taken inresponse to the remote access. The indication of the source ID may beused to send the result of the operation back to the remote terminalwherefrom the request for a remote access originated.

As shown in FIG. 22, at least one functional unit 156 coupled to theremote access network 154 supports a data base 158 registering theavailability and position of different remote devices in themanufacturing field. This information may then be used to forwardmessages between the different remote devices or from a systemcontroller to an operator carrying a remote device or vice versa.

While in the above, the described techniques have been described withreference to schematic and circuit diagrams of various implementationsof the field device, it should be noted that clearly the describedtechniques may also be implemented using the method of data exchangedigitally using a microcontroller. In this case, the describedtechniques may be implemented as a computer program product directlyloadable into the internal memory of the microcontroller comprisingsoftware code portions for implementing the method.

A number of implementations have been described. Nevertheless, it willbe understood that various modifications may be made. Accordingly, otherimplementations are within the scope of the following claims.

1. A field device comprising: at least one actuator and/or sensorconfigured to alter and/or sense a control and/or process variable in amanufacturing field; a wireless transmitter and/or receiver configuredfor wireless data communication between the field device and a remotedevice when activated; an interface configured to receive operatingpower; an energy buffer configured to store energy from the receivedoperating power and to supply the stored energy to the wirelesstransmitter and/or receiver during wireless data communication; and acontroller configured to evaluate the stored energy available in theenergy buffer prior to activation of the wireless transmitter and/orreceiver and delay activation of the wireless transmitter and/orreceiver when the evaluation indicates that the stored energy in theenergy buffer is insufficient to sustain operation of the wirelesstransmitter and/or receiver during wireless data communication.
 2. Thefield device of claim 1 wherein the controller is configured to split aninput data stream into a plurality of data segments for subsequentwireless data transmission.
 3. The field device of claim 2 wherein thecontroller is configured to evaluate the stored energy for each one ofthe plurality of data segments.
 4. The field device of claim 1 whereinthe wireless transmitter and/or receiver comprises an infraredtransmitter, the infrared transmitter comprising: a light emitting unitconnected to a power supply line and to ground and emitting infraredwaveforms according to driving pulses outputted by a coder unit; andwherein the energy buffer is coupled across the light emitting unit tosupply energy to the light emitting unit.
 5. The field device of claim 4further comprising a first resistor and a second resistor connected inseries between the power supply line and the light emitting unit,wherein the energy buffer is connected to a node between the firstresistor and the second resistor, the first resistor being configured tolimit a charge current of the energy buffer.
 6. The field device ofclaim 5 wherein the second resistor is variable to change the irradianceof the light emitting unit according to a predetermined data exchangedistance.
 7. The field device of claim 1 wherein the energy buffercomprises a capacitor.
 8. The field device of claim 1 wherein thecontroller comprises a voltage monitor to evaluate the energy stored inthe energy buffer.
 9. A method for exchanging data in a manufacturingplant control system using wireless data communication, the methodcomprising: receiving operating power at a field device that includes awireless transmitter and/or receiver; storing, at the field device,energy from the received operating power; evaluating the stored energyprior to activation of the wireless transmitter and/or receiver; anddelaying activation of the wireless transmitter and/or receiver when theevaluation indicates that the stored energy in the energy buffer isinsufficient to sustain operation of the wireless transmitter and/orreceiver during wireless data communication.
 10. The method of claim 9further comprising splitting an input data stream into a plurality ofdata segments for subsequent wireless data transmission.
 11. The methodof claim 10 wherein evaluating the stored energy prior to activation ofthe wireless transmitter and/or receiver comprises evaluating the storedenergy for each one of the plurality of data segments.
 12. The method ofclaim 9 wherein evaluating the stored energy prior to activation of thewireless transmitter and/or receiver comprises evaluating the storedenergy using a voltage monitor.
 13. The method of claim 9 whereinstoring, at the field device, energy from the received operating powercomprises storing the energy in an energy buffer.
 14. The method ofclaim 13 wherein the energy buffer comprises a capacitor.
 15. The methodof claim 9 further comprising activating the wireless transmitter and/orreceiver for wireless data communication.
 16. The method of claim 15further comprising providing the stored energy to the wirelesstransmitter and/or receiver from the energy buffer during wireless datacommunication.
 17. A computer-useable storage medium storing a programthat is loadable into a memory of a field device, wherein the fielddevice stores energy from received operating power, the programincluding software code for exchanging data in a manufacturing plantcontrol system using a wireless transmitter and/or receiver of the fielddevice by causing a controller of the field device to: store, at thefield device, energy from the received operating power; evaluate thestored energy prior to activation of the wireless transmitter and/orreceiver; and delay activation of the wireless transmitter and/orreceiver when the evaluation indicates that the stored energy in theenergy buffer is insufficient to sustain operation of the wirelesstransmitter and/or receiver during wireless data communication.
 18. Themedium of claim 17 wherein the program includes software code forcausing the controller of the field device to split an input data streaminto a plurality of data segments for subsequent wireless datatransmission.
 19. The medium of claim 18 wherein, to evaluate the storedenergy prior to activation of the wireless transmitter and/or receiver,causing a controller of the field device to evaluate the stored energyfor each one of the plurality of data segments.
 20. The medium of claim17 wherein the program includes software code for causing a controllerof the field device to provide the stored energy to the wirelesstransmitter and/or receiver during wireless data communication.